build: fix generate_protos session

[busunkim96]

Uncomment generate_protos and clone api-common-protos inside the session so it can be run in autosynth.

Fixes #27 🦕

Verify locally by doing nox -s generate_protos (no additional setup should be required)

[parthea]

LGTM

Local output:

(gapicgen) partheniou@partheniou-vm-1:~/git/python-access-context-manager$ nox -s generate_protos -r
nox > Running session generate_protos
nox > Re-using existing virtualenv at .nox/generate_protos.
nox > pip install grpcio-tools
nox > git -C api-common-protos pull
fatal: cannot change to 'api-common-protos': No such file or directory
nox > Command git -C api-common-protos pull failed with exit code 128
nox > git clone --single-branch https://github.com/googleapis/api-common-protos
Cloning into 'api-common-protos'...
remote: Enumerating objects: 43, done.
remote: Counting objects: 100% (43/43), done.
remote: Compressing objects: 100% (25/25), done.
remote: Total 1141 (delta 34), reused 18 (delta 18), pack-reused 1098
Receiving objects: 100% (1141/1141), 341.50 KiB | 7.59 MiB/s, done.
Resolving deltas: 100% (654/654), done.
nox > python -m grpc_tools.protoc --proto_path=api-common-protos --proto_path=. --python_out=. google/identity/accesscontextmanager/v1/access_policy.proto google/identity/accesscontextmanager/v1/service_perimeter.proto google/identity/accesscontextmanager/v1/access_level.proto google/identity/accesscontextmanager/type/device_resources.proto
google/identity/accesscontextmanager/v1/access_policy.proto:20:1: warning: Import google/api/annotations.proto is unused.
google/identity/accesscontextmanager/v1/service_perimeter.proto:20:1: warning: Import google/api/annotations.proto is unused.
google/identity/accesscontextmanager/type/device_resources.proto:19:1: warning: Import google/api/annotations.proto is unused.
google/identity/accesscontextmanager/v1/access_level.proto:22:1: warning: Import google/api/annotations.proto is unused.
nox > Session generate_protos was successful.